Contact lens having an index of refraction approximating that of human tears

ABSTRACT

A wettable contact lens of the type applied to the human eye to correct vision deficiencies, said lens formed of a transparent, dimensionally stable, solid material characterized by an index of refraction approximating that of the human tears.

BACKGROUND OF THE INVENTION

Although known and used for some years, contact lenses have not achievedfull acceptance by most members of the public having vision difficultiesrequiring correction. Contact lenses of the scleral type cover asubstantial area of the eye during use, thereby sealing off circulationof tears and the atmosphere. This causes partial asphyxiation whichaffects the metabolism and vision of the eye. The more recent corneallenses, because of their relatively smaller size and lighter weight,usually cause less irritation to the cornea, and have achieved greateracceptance. However, the "break-in" period necessary to accustom thecornea of the wearer to support a corneal lens, while varying fromperson to person, depending upon the individual's sensitivity of thecornea, usually extends over a considerable period of time. Some personshave found contact lenses to be intolerable because of the eyeirritation resulting during and after any extended period of continuouswear.

Effort has been made to design both scleral and corneal lenses to fitmore comfortably. For example, U.S. Pat. Nos. 2,240,157-Gagnon et al and2,330,837-Mullen suggest methods for producing a scleral lens in whichthe scleral band fits the contour of the eye of the wearer. However, thecorneal portion of the lens clears the cornea and limbus, so that thelens never contacts the cornea when worn. Such lenses have generallyrequired the use of an accessory fluid in the space between the corneaand the ground-out corneal area of the lens. Application of such lensesto the eye is difficult and painful, and they have not achieved widepopularity.

It has been suggested that eye irritation could be reduced by designingthe contact lenses with various radii of curvature. U.S. Pat. No.2,544,246-Butterfield suggests that the corneal lens have an innerspherical central area and an outer marginal portion formed by a seriesof separate and distinct steps to introduce a parabolic fit. U.S. Pat.No. 2,510,438-Tuohy, discloses a contact lens having a radius ofcurvature on its concave side slightly greater than the radius ofcurvature of the cornea, with an increasing clearance at the marginalareas of the lens. Feinbloom U.S. Pat. No. 3,227,507 discloses theproduction of a corneal contact lens having an inner ellipsoidalsurface. While lenses disclosed in the foregoing patents offer animprovement over scleral type lenses, they nevertheless tend to causeconsiderable irritation to the eye, and on the average cannot be worn inexcess of ten hours.

Use of softer material in the production of contact lenses to provide amore comfortable lens has also been suggested. U.S. Pat. No.3,228,741-Becker discloses the use of a filler, transparent, hydrocarbonsubstituted polysiloxane rubber as a contact lens material. Lenses ofthis material are said to possess a softness similar to that of theupper lid of the human eye, a high permeability to carbon dioxide,oxygen, and water vapor, and an index of refraction ranging from 1.49 to1.56, depending upon the amount of filler material used. Because oftheir soft, elastic characteristics, such materials do not lendthemselves to consistent production of high quality contact lenses, norare they dimensionally stable.

Wichterle et al. U.S. Pat. No. 3,220,960, discloses a hydrogel materialconsisting of from 20 to 90 percent of an aqueous liquid, and across-linked hydrophilic polymer. However, lenses made of such materialsare handicapped by optical problems. Notably, the effective power of thelens changes as it is worn. Also, such lenses may be torn easily whilein the hydrated state, or broken in the dehydrated state, thus adding ahandling problem to their use. Moreover, such porous hydrogels arereceptive to bacterial invasion and proliferation. Despite assertions tothe contrary, it has been found that such hydrogel materials do notafford extended periods of comfortable wear in a high percentage ofcases. An excellent discussion of the disadvantages of such lenses isfound in Precision-Cosmet Digest, Vol. 5, No. 9, April 1965.

Due to the limitations of the foregoing materials, contact lenses incommercial use at this time are almost universally manufactured frompolymethyl methacrylate, an optically clear, moldable, synthetic polymermaterial characterized by an index of refraction of 1.49. However, as aresult of the problems noted above in producing a lens which fitscomfortably, lenses made from polymethyl methacrylate can be worn onlyfor relatively limited periods of time.

It is therefore a primary object of the invention to provide an improvedcontact lens.

Another object of the invention is to provide a contact lens whichaffords a comfortable fit, and which may be worn for extended periods oftime without causing irritation to the eye.

Yet another object of the invention is to provide a contact lens havingan index of refraction approaching that of human tears.

A further object of the invention is to provide a contact lens whoseposterior surface conforms with the anterior surface of the human corneaand/or sclera.

It is still another object of the invention to provide a contact lenswhich significantly diminishes the aberrations due to reflected lightoccurring with conventional contact lenses of the prior art.

SUMMARY OF THE INVENTION

It has now been discovered that contact lenses which can be worncomfortably over extended periods of time are attained if a wettablelens is fabricated from a transparent, dimensionally stable, solidmaterial characterized by an index of refraction approximating that ofthe human tear. This may be achieved in accordance with one aspect ofthe present invention by providing a contact lens of such a material inwhich the posterior surface of the lens conforms with the varyingtopography of the anterior segment of the human cornea and/or sclera.

The present invention takes advantage of the fact that differencesbetween the indices of refraction on either side of an interface of agiven curvature will result in a refractive or vergence power change atthis interface depending upon the curvature and the indices ofrefraction. The refractive indices of the synthetic polymer materialsmost widely used as contact lenses vary from a low of 1.49 to a high ofabout 1.55. However, the total or combined index of refraction of theeye as an optical instrument averages to about 1.3375, or almost equalto that of the human tears (1.336).

The significant difference between the index of refraction of the eyeand that of the material of which present lenses are composed limits thenumber of modifications, or so-called fitting curves which may be placedon the posterior aspect of the lens before the optical quality of thelens is impaired. Thus, when contact lenses made of a material having ahigher index of refraction than the cornea are modified excessivelywithin the optical zone of the lens, the resulting aberration due to thedifference between the indices of refraction will significantly alterthe visual acuity. This is particularly true in the case offlush-fitting therapeutic lenses where the curvature markedly departsfrom sphericity.

It has now been discovered that by using a transparent, dimensionallystable, solid material, characterized by an index of refractionapproximating the index of refraction of the human tears and "workable"to the extent that it can be either molded or ground into a lens, anynumber of fitting curves or modifications can be made on the posterioraspect of the lens in order to give the best lens-corneal relationshipand thus provide the optically perfect lens. The only opticalrequirement of lenses made in accordance with the invention is that thefront surface of the lens be characterized by a curve of such powernecessary to correct the refractive error of the eye. In air, lenses ofthe invention are aberrated when the anterior surface is spherical andthe posterior surface is aspherical or irregular, i.e., conforms withthe varying topography of the anterior segment of the human corneaand/or sclera. However, once the irregularity of the posterior surfaceis optically eliminated by placing it in contact with a medium ofsimilar index of refraction, as for example the tear film, theaberrations optically disappear.

The present invention affords the production of contact lenses of boththe corneal and scleral type which may be worn for periods of timeconsiderably exceeding the average 10 hour period which ischaracteristic of conventional lenses of the prior art in accordancewith the invention, "flush-fitting" lenses can be provided whoseposterior surfaces precisely match the contour of the cornea of thewearer, thus affording a perfect, and hence comfortable fit.

In addition, lenses may be constructed in accordance with the inventionin which the posterior aspects of the lenses are ground or molded bystandard methods to provide an optical curve thereon. While such lensesdo not afford the full advantages of comfort of the "flush-fitting"lenses, they nevertheless exhibit a marked improvement over theconventional lenses of the prior art. Notably, and quite unexpectedly ithas been found that such lenses manufactured in accordance with theinvention considerably diminish, and in some cases eliminate, theaberrations due to reflected light as manifested by halos, glare andstreamers which normally occur with conventional prior art contactlenses when the wearer is exposed to bright lights shining into theeyes.

A critical feature of the invention is that the lenses thereof beconstructed from a transparent, dimensionally stable, solid materialcharacterized by an index of refraction approximating that of humantears. The transparency of the material should be adequate to assuregood vision of the wearer of the lens, although the material need notnecessarily be crystal clear. Materials having transparencycharacteristics similar to polymethyl methacrylate are preferred.

The refractive index of the material suitable for use in the practice ofthe invention should approximate that of human tears, i.e., must be nogreater than 1.40. It is preferred, however, that the materials exhibitindices of refraction more nearly approaching the value of 1.336, theindex of refraction of human tears. Generally speaking, when lenses areproduced which are characterized by posterior surfaces matching thetopography of the cornea of the wearer, indices of refraction of below1.37 are preferred. Of course, optimum results are achieved when thematerial used exhibits an index of refraction below 1.34 and approachesthe value characteristic of human tears (1.336).

Materials useful in the practice of the invention must also becharacterized by good dimensional stability under the conditionsnormally encountered in the manufacture and use of the contact lensesmade therefrom. In this connection it is important that the materialsretain their dimensional stability under conditions that would beencountered when the lenses are removed from the eye and stored. Thus,the materials contemplated herein differ significantly from hydrogelmaterials which lose their dimensional stability when taken out of anaqueous environment.

The materials used to provide lenses in accordance with the inventionshould also be solid, i.e., have a Knoop hardness of at least 2, andpreferably should be characterized by a hardness of 4 or more in orderto facilitate the manufacture of contact lenses by the conventionalmethods known in the art. Of course, it is essential that the materialsexhibit nontoxic properties so as to be compatible with the livingtissue of the human eye.

Included among the materials which can be used in the practice of theinvention are the terpolymers ofhexafluoroacetone-tetrafluoroethylene-ethylene (HFA/TFE/E terpolymers)obtained from a reaction medium containing ethylene andtetrafluorethylene in 1:1 molar ratio and hexafluoroacetone in largemolar excess, with the hexafluoroacetone as a complex with ROH in whichthe molar ratio of ROH with hexafluoroacetone may vary from 0.8-2.5 Rmay be hydrogen or alkyl.

Such HFA/TFE/E terpolymers have been found to be characterized by anindex of refraction of the order of 1.39 and a Knoop hardness of about8.6. Contact lenses in accordance with the invention can be molded orground from such materials by methods well known to those skilled in theart.

A further class of materials useful in the practice of the inventioninclude the polyperfluoroalkylethyl methacrylates of the type disclosedin U.S. Pat. No. 3,282,905, Fasick et al. Such methacrylates have beenproduced exhibiting indices of refraction of the order of 1.368-1.374and a Knoop hardness of above 2. Such polymers are characterized byexcellent clarity and are moldable at 130°-140° C.

By far the most preferred materials for use in the production of lensesin accordance with the invention are the copolymers and terpolymers ofperfluoro-2-methylene-4-methyl-1.3-dioxolane, referred to hereinafter asPMD. The preparation of PMD as well as copolymers thereof is describedin U.S. Pat. Nos. 3,307,330, Niedzielski et al. and 3,308,107, Selman etal. The refractive index of PMD homopolymer is in the range of1.3308-1.3345, or somewhat below the optimum value of 1.336, the indexof refraction of human tears. It has been found in this respect that thecopolymers of PMD and tetrafluorethylene provide materials which areespecially suitable in the practice of the present invention in thatthey exhibit refractive indices in the desired range, are characterizedby good clarity, absence of color and haze, and further exhibit goodhardness properties. As noted in the patent to Niedzielski et al.(3,307,330), such copolymers also exhibit permeability to oxygen andcarbon dioxide. Accordingly, when contact lenses constructed of suchmaterials are worn, oxygen and carbon dioxide are circulated through thelens, as well as underneath and around it, thus increasing the nutritionof the cornea. It has been found that a copolymer containing 92 parts byweight of tetrafluoroethylene with eight parts by weight of PMD wascharacterized by an index of refraction of 1.349 and a Knoop hardness of4.9. The molding temperature of the copolymer was 350° C. In thisrespect, copolymers of PMD and tetrafluoroethylene characterized byoptimum indices of refraction and lower molding temperatures as well ashigher values of Knoop hardness may be prepared by copolymerizing from10 to 20 weight percent of tetrafluoroethylene with from 80 to 90 weightpercent of PMD.

It is essential that the lenses made in accordance with the invention bewettable by human tears. In this respect wettability may be determinedby placing a drop of liquid on the substance whose wettability is to betested and observing and measuring the receding and advancing contactangles, i.e., the angles the liquid makes on the solid surface at thethree phase boundary as measured through the liquid in order for thematerial to be designated "wettable" the receding angle must be 0° andthe advancing angle must be less than 90°.

While many of the materials useful in the practice of the invention mayexhibit inherent wettability, as for example, the HFA/TFE/E terpolymermentioned above, it may be necessary to impart wettability to thesurface of contact lenses made from other materials useful in thepractice of the invention which do not exhibit wettability. All of thematerials mentioned above can be treated to impart wettability, and thusrender the surfaces of contact lenses made therefrom hydrophilic. Thismay be achieved with some polymers by treating the materials with awetting agent such as, for example, a 0.04 percent aqueous solution ofalkyldimethylbenzylammonium chloride. Such treatment simply involvesapplying the wetting solution onto the lens or polymer surface andsubsequently washing the lens with water to remove the applied solution.If a continuous film of water remains, the polymer wets satisfactorily.If beading occurs, wettability is questionable. Polymethyl methacrylatelenses of the type conventionally used are wetted by this procedure, andremain wettable after being placed in the eye. Other materials, notablythe TFE/PMD copolymers and polyperfluoroalkyl ethyl methacrylatesrequire a more vigorous treatment, such as exposure to corona dischargeor a sodium etchant, to attain wettability. Other means for renderingcontact lenses of the present invention wettable will readily occur tothose skilled in the art.

Contact lenses of the invention may be produced from the above materialsby the use of commercial contact lens grinding equipment and techniqueswell known to those skilled in the art. The lenses may be molded,machined and polished by known methods. In the event it is desired toproduce a flush-fitting lens, i.e., a lens whose posterior surfaceprecisely matches the varying topography of the cornea of the eye, themolding technique described in the article "Flush-Fitting ScleralContact Lenses" appearing in the American Journal of Opthalmology,Volume 61, No. 5, Part II, May, 1966, may be used. Flush-fitting sclerallenses produced by that method are direct copies of the anterior segmentof the eye, including both cornea and sclera, and follow in detail thesurface contour of both. Only a capillary layer of tears separates thelens thus formed from the eye. Flush-fitting corneal lenses may beobtained by using the foregoing method to provide a flush-fitting lens,and thereafter cutting away the scleral band. The edges of the remainingcorneal portion may then be machined to provide comfortable fit.

DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS

For further objects and advantages of the invention and for a moredetailed discussion of preferred embodiments thereof, reference is to behad to the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a vertical cross section of a portion of a human eye to whichthere has been applied a scleral contact lens of the type disclosed inthe prior art;

FIG. 2 is a vertical sectional view of a portion of the human eye towhich there has been applied a contact lens embodying one form of thepresent invention;

FIG. 3 is a vertical section of a portion of the human eye to whichthere has been applied a contact lens embodying another form of theinvention; and

FIG. 4 is a vertical section of a portion of the human eye to whichthere has been applied a contact lens forming still another embodimentof the invention.

Referring now to FIG. 1, the standard scleral contact lens 10 of thekind disclosed in the prior art, when fitted to the human eye 12,parallels the curvature of the anterior sclera 14 and then vaults thecornea 16, leaving between the anterior surface 18 (whose irregularcontour has been exaggerated) of the cornea 16 and the posterior surface20 of the lens 10 a space 22 filled with tears or a buffered solution.The posterior surface 20 of the contact lens 10 is an optical surfacewhich, with the anterior curvature 24 of the lens, provides opticalcorrection to the eye 12.

FIG. 2 illustrates a scleral contact lens 30 forming one embodiment ofthe invention. Lens 30 is of generally concavo-convex cross section andis constructed of a transparent, dimensionally stable solid materialcharacterized by an index of refraction approximating that of humantears. By virtue of the fact that the index of refraction of thematerial of which the lens 30 is composed approaches that of the tearfilm of the eye 32, the lens 30 may be constructed such that it isflush-fitting, i.e., the posterior segment 34 follows in exact detailthe irregular surface contour 36 of the anterior segment of the eye,including both the cornea 38 and the sclera 40. Only a capillary layerof tears separates the lens from the eye. Thus the lens shown in FIG. 2does not include an optical surface on its posterior base 34. Since theposterior aspect of the lens 30 matches in detail the surface contour ofthe cornea 38 and sclera 40 of the eye, it provides virtually a "glovefit." Optical correction is achieved by grinding a power surface on theinterior surface 41 of the lens 30. Such a lens is most satisfactoryfrom the wearer's standpoint and can be worn continuously for periods oftime well exceeding 10 hours.

In FIG. 3, a "flush-fitting" corneal contact lens 60 of the invention isshown fitted to a human eye. Lens 60 of generally concavo-convex crosssection is constructed of a material characterized by an index ofrefraction approaching that of human tears, i.e., not greater than 1.40and preferably of a value more closely approximating 1.336. Theposterior surface 62 of the corneal lens 60 conforms with the topographyof the anterior segment 64 of the eye 66. Such a corneal lens 60 may beconstructed by cutting away the scleral band of a flush-fitting sclerallens such as shown in FIG. 2, and subsequently smoothing the edges 68 ofthe corneal portion to provide a comfortable fit.

FIG. 4 illustrates a generally concavo-convex contact lens 80 of theinvention having both its posterior surface 84 as well as its anteriorsurface 86 ground to provide optical correction. The lens 80 thusdiffers from the flush-type lenses shown in FIGS. 2 and 3. While thelenses of the type shown in FIG. 4 do not provide as comfortable a fitas those illustrated in FIGS. 2 and 3 and for the reason that theirposterior surfaces do not conform precisely with the anterior surfacecontour of the cornea 88, the lenses nevertheless are a markedimprovement over the conventionally available corneal contact lenses inthat they significantly diminish and often eliminate the aberrations dueto reflected light, as manifested by halos, glare and streamers whichnormally occur with conventional contact lenses when the wearer isexposed to bright lights shining into the eyes, as may occur duringnight driving. The lens shown in FIG. 4 can be constructed from thematerials contemplated for use in accordance with the invention bymethods and procedures well known to those skilled in the art. Ifdesired, the lens 80 may be provided with minute channels or holes 90 topermit transport of tears and oxygen to the cornea. Such channels may bedrilled in the lens by conventional methods without detracting from theoptical properties of the lenses.

Generally speaking, lenses of the type illustrated in FIGS. 1-3 will beformed of polymer films having thicknesses varying from about 3 to about25 mm. Preferably, the lenses will have a thickness of the order of0.1-0.2 mm. minus lenses, and 0.15-0.50 mm. plus lenses.

The method of molding contact lenses of the type illustrated in FIGS. 2and 3 can be the same as has been used in the past for standard sclerallenses. However, the subsequent manufacturing technique differsconsiderably from past methods since the posterior surface of a lensmade in accordance with the invention is not modified into an opticalsurface as in a standard scleral lens, but remains a perfect replica ofthe cornea and sclera.

As mentioned above, a molding method which can be used to prepare aflush-fitting scleral contact lens of the invention is described inVolume 61, No. 5, Part II of the May, 1966, issue of the AmericanJournal of Ophthalmology. Generally speaking, this method involvesfitting a plastic casting shell device onto the eye, through the stem ofthe funnel is injected the impression material consisting of an opaque,rather viscous liquid prepared by mixing an alginate powder with water.An example of such a material is ophthalmic Moldite, a productmanufactured by Obrig Laboratories, New York, N.Y., and consisting of analginate gelling agent which reacts when mixed with water. Gelling ofthe material is retarded by an added preparation which gives sufficienttime for the material to be placed on the eye and the molding shellcentered.

After the alginate material is injected into the funnel and onto theeye, sufficient time (about 3 minutes) is permitted to elapse to permitthe liquid to set to a gell impression which is then removed from theeye. A mixture is prepared from water and powdered plaster castingmaterial and is then poured into the moist soft alginate impressionstill attached to the funnel. The alginate mold is vibrated while themixture is poured into it, to prevent formation of bubbles. After aboutten minutes, the stone mold has hardened enough so that it can bestripped from the alginate. The resulting stone mold can then be used tomake the lens into a negative replica of the anterior corneal andscleral surfaces.

Flush-fitting scleral contact lenses of the invention may then beproduced by heating a sheet of material characterized by an index ofrefraction approaching that of human tears to a temperature sufficientlyhigh to permit the sheet material to conform to the surface of the moldupon the application of pressure. After cooling, the resulting lens istaken from the die and the anterior surface machined and polished toprovide the desired optical surface.

As above noted, a flush-fitting corneal lens, as illustrated in FIG. 3,can be prepared by cutting away the scleral band of the flush-fittingscleral lens, and treating the edges of the corneal lens so that acomfortable fit may be attained.

As will be appreciated by those skilled in the art, it is also possibleto prepare contact lenses in accordance with the invention through theuse of conventionally available measuring devices such as theRadioscope, the Keratometer and the Toposcope. While such devices may beused to produce contact lenses whose posterior portions closelyapproximate the anterior segment of the eye, such lenses will notprovide as satisfactory a fit as will be obtained from the flush-fittinglenses described above.

In order that those skilled in the art may better understand how thepresent invention may be practiced, the following examples are given byway of illustration and not by way of limitation. The lenses of examples1-3 inclusive were prepared from the respective polymer films which wereheated to their softening temperature and subsequently draped over thestone mold of a patient's eye. A female mold roughly conforming to theshape of the stone mold was then quickly pressed onto the polymer filmand held tightly against it until the polymer hardened. Except for theHFE/TFE/E terpolymer (which was found to be inherently hydrophilic) thelenses constructed from the other polymers were treated to impartwettability.

EXAMPLE 1

A terpolymer was prepared by reacting hexafluoroacetone,tetrafluoroethylene and ethylene in a mole ratio of 1.6:1.0:1.0, thehexafluoroacetone being in the form of a 1:1 mol complex with methanol.The resulting polymer was characterized by an index of refraction of1.392, a Knoop hardness of 8.6 and a molding temperature of 230° C. Aspreviously mentioned, the polymer exhibited inherent wettability. A goodscleral lens was molded from this polymer and appeared frosted, due tothe irregular contour of the posterior surface of the lens. Thisfrosting was substantially reduced when the lens was placed in water.

EXAMPLE 2

A scleral lens was molded from polyperfluoroalkylethyl methacrylate ofthe formula ##STR1##

The polymer was obtained by polymerizing a mixture of monomers of theabove formula in which mixture the monomer weight fractions were asfollows: n=1, 1 percent; n=2, 50 percent; n=3, 35 percent; n=4, 7percent; n=5, 1 percent. The resulting polymer had an index ofrefraction of 1.374 and a Knoop hardness of 2.03. Its moldingtemperature was about 130° C. A good scleral lens was produced from thispolymer which appeared partly frosted on its posterior side and wasopaque when viewed in air. However, the lens became fairly transparentwhen placed in water.

EXAMPLE 3

By the method outlined above, a scleral lens was obtained from apolyperfluoroalkylethyl methacrylate of the formula set forth above inwhich n equaled 3. The resulting polymer was characterized by an indexof refraction of 1.368, a Knoop hardness of 2.08 and a moldingtemperature of 140° C. A good scleral lens was obtained from thematerial. The posterior aspect of the lens appeared frosted and thefront surface was fairly smooth. The lens was opaque when viewed in airbut became essentially clear when immersed in water.

EXAMPLE 4

A contact lens was prepared from a copolymer of tetrafluoroethylene andperfluoro-2-methylene-4-methyl-1.3-dioxolane (PMD). The refractive indexof the copolymeric material was 1.3380 and the Knoop hardness was 4.9.

By virtue of the present invention there are provided contact lenseswhich are significantly improved over the lenses disclosed in the priorart. Notably, the contact lenses of the invention, by virtue of beingconstructed of materials characterized by indices of refractionapproximating that of human tears, can be contour fitted to the eye toprovide a perfect fit and thus enable the lenses to be worn for periodsof time considerably exceeding the periods during which conventionallenses may be worn. Furthermore, the lenses of the invention have beenfound to reduce and often eliminate the aberrations due to reflectedlight which occur with ordinary contact lenses.

It should be understood that while the present invention has beendescribed in considerable detail with respect to certain specificembodiments thereof, it is not to be considered limited to thoseembodiments, but may be used in other ways without departure from thespirit of the invention or the scope of the appended claims.

We claim:
 1. A contact lens for providing optical correction to a humaneye, said lens having a generally concavo-convex cross section with theconcave surface adjacent to the eye and comprising a transparent,dimensionally stable, nontoxic polymer characterized by an index ofrefraction no greater than 1.40 and closely matching the index ofrefraction of human tears, and selected from the group consisting ofpolymers of hexafluoroacetone-tetrafluoroethylene-ethylene, polymers ofperfluoroalkylethyl methacrylates, and polymers ofperfluoro-2-methylene-4-methyl-1.3-dioxolane.
 2. The contact lens ofclaim 1 in which the posterior surface of said lens conforms with thetopography of a human eye, and said polymer is characterized by an indexof refraction of no greater than 1.37.
 3. The contact lens of claim 2 inthe form of a scleral lens.
 4. The contact lens of claim 1 characterizedby an index of refraction no greater than 1.35.
 5. The contact lens ofclaim 1 in which said transparent dimensionally stable, nontoxic polymercomprises a polymer of hexafluoroacetone-tetrafluoroethylene-ethylene.6. The contact lens of claim 1 in which said transparent, dimensionallystable, nontoxic polymer comprises a polymer of a perfluoroalkylethylmethacrylate.
 7. The contact lens of claim 6 in which the transparent,dimensionally stable, nontoxic polymer comprises a polymerizedperfluoroalkylethyl methacrylate in which the alkyl group contains from.Badd..[.3 to 14.]..Baddend. .Iadd.4 to 12 .Iaddend.carbon atoms.
 8. Thecontact lens of claim 7 in which the transparent, dimensionally stable,nontoxic polymer comprises a polymerized perfluoroalkylethylmethacrylate in which the alkyl group contains .Badd..[.3.]..Baddend..Iadd.8 .Iaddend.carbon atoms.
 9. The contact lens of claim 1 in whichsaid transparent, dimensionally stable, nontoxic polymer comprises apolymer of perfluoro-2-methylene-4-methyl-1.3-dioxolane.
 10. The contactlens of claim 9 in which the transparent, dimensionally stable, nontoxicpolymer comprises a copolymer of perfluoro(2-methylene-4-methyl-1.3-dioxolane) and tetrafluoroethylene.
 11. Thecontact lens of claim 10 in which said copolymer is composed of from 50to 95 percent by weight of perfluoro(2-methylene-4-methyl-1.3-dioxolane) and from 5 to 50 percent by weightof tetrafluoroethylene. .Iadd.
 12. A solid, dimensionally stable cornealcontact lens for providing optical correction to a human eye; said lenscomprising a transparent, dimensionally stable non-toxic polymer andbeing characterized by reduced aberrations due to reflected light; saidlens having both an anterior surface and a posterior surface shaped toprovide optical correction; said lens having a refractive index nogreater than 1.40 and having sufficient permeability to oxygen andcarbon dioxide to permit circulation therethrough for nutrition of thecornea. .Iaddend..Iadd.
 13. The contact lens defined in claim 12 whereinsaid lens has a Knoop hardness of at least
 2. .Iaddend..Iadd.
 14. Thecontact lens defined in claim 12 wherein said lens has a Knoop hardnessof at least
 4. .Iaddend..Iadd.
 15. The contact lens defined in claim 12wherein said lens includes minute holes to permit transport of oxygen tothe cornea. .Iaddend. .Iadd.
 16. The contact lens defined in claim 12wherein said polymer has sufficient permeability to oxygen and carbondioxide to permit circulation therethrough for nutrition of the cornea..Iaddend..Iadd.
 17. The contact lens defined in claim 12 wherein theperiphery of the lens is rounded to provide a comfortable fit. .Iaddend..Iadd.
 18. The contact lens defined in claim 12, wherein said lens has arefractive index closely matching the index of refraction of humantears. .Iaddend.